"[...] In areas like SF, the sale of high-end properties is a form of vanity and ego for the sellers, so they love to show off the home, especially to the neighbors. Then there is the issue of competition — if your competitor holds his/her listings open, you must also do so, otherwise risking the question from your client:
'Why not?'

Finally, the new(er) generation of buyers have already done their homework, have viewed the listings from the privacy of their desktop computers or smart phones and will only go look at a very, very select few homes and not in the company of a public open. As the marketing becomes more sophisticated, with high-end photography (perhaps including aerial via drone) and increasingly with VR tech, opens will truly be outdated."